"If you want to test a man's character, give him power," said Abraham Lincoln. It's a truism that power magnifies personality -- but is it true? A new study says no. "Before, people thought that disposition is linked to will; it's mainly internally driven," says University College London psychologist Ana Guinote, who conducted the study with Mario Weick of the University of Kent and London doctoral student Alice Cai. "Our findings show that the environment crucially triggers dispositional or counter-dispositional behavior in powerful people."